Electrochemistry of free chlorine and monochloramine and its relevance to the presence of Pb in drinking water

The commonly used disinfectants in drinking water are free chlorine (in the form of HOCl/OCl-) and monochloramine (NH2Cl). While free chlorine reacts with natural organic matter in water to produce chlorinated hydrocarbon byproducts, there is also concern that NH2Cl may react with Pbto produce soluble Pb(II) products--leading to elevated Pb levels in drinking water. In this study, electrochemical methods are used to compare the thermodynamics and kinetics of the reduction of these two disinfectants. The standard reduction potential for NH2Cl/Cl- was estimated to be +1.45 V in acidic media and +0.74 V in alkaline media versus NHE using thermodynamic cycles. The kinetics of electroreduction of the two disinfectants was studied using an Au rotating disk electrode. The exchange current densities estimated from Koutecky-Levich plots were 8.2 x 10(-5) and 4.1 x 10(-5) A/cm2, and by low overpotential experiments were 7.5 +/- 0.3 x 10(-5) and 3.7 +/- 0.4 x 10(-5) A/cm2 for free chlorine and NH2Cl, respectively. The rate constantforthe electrochemical reduction of free chlorine at equilibrium is approximately twice as large as that for the reduction of NH2Cl. Equilibrium potential measurements show that free chlorine will oxidize Pb to PbO2 above pH 1.7, whereas NH2Cl will oxidize Pb to PbO2 only above about pH 9.5, if the total dissolved inorganic carbon (DIC) is 18 ppm. Hence, NH2Cl is not capable of producing a passivating PbO2 layer on Pb, and could lead to elevated levels of dissolved Pb in drinking water.     

Mechanism and kinetics of cyanogen chloride formation from the chlorination of glycine

Glycine is an important precursor of cyanogen chloride (CNCl)--a disinfection byproduct (DBP) found in chlorinated drinking water. To model CNCl formation from glycine during chlorination, the mechanism and kinetics of the reaction between glycine and free chlorine were investigated. Kinetic experiments indicated that CNCI formation was limited by either the decay rates of N,N-dichloroglycine or a proposed intermediate, N-chloroiminocarboxylate, CIN=CHCO2-. Only the anionic form of N,N-dichloroglycine, NCl2CH2CO2-, however, decays to form CNCl, while the protonated neutral species forms N-chloromethylimine. At pH > 6, glycine-nitrogen is stoichiometrically converted to CNCI, while conversion decreases at lower pH due to the formation of N-chloromethylimine. Under conditions relevant to drinking water treatment, i.e., at pH 6 to 8 and with free chlorine in excess, a simplified rate expression for the concentration of glycine-nitrogen converted to CNCl, [CNCl]f, applies: dt/d[CNCl]f = k2*[Cl2-Gly](T,o)exp(-k2*t) where [Cl2-Gly]T,o is the initial concentration of total N,N-dichloroglycine, k2* is the first-order decay constant for CIN=CHCO2-, k2*(s(-1)) = 10(12)(+/-4) exp(-1.0(+/-0.3) x 10(4)/T), and T is the absolute temperature in K. Kinetic expressions for d[CNCl]/dt when free chlorine is in excess, however, must also account for the significant decay of CNCl by hypochlorite-catalyzed hydrolysis, which has been characterized in previous studies. Although CNCl formation is independent of the free chlorine concentration, higher chlorine concentrations promote its hydrolysis.     

Nitryl chloride and molecular chlorine in the coastal marine boundary layer

The magnitude and sources of chlorine atoms in marine air remain highly uncertain but have potentially important consequences for air quality in polluted coastal regions. We made continuous measurements of ambient ClNO(2) and Cl(2) concentrations from May 15 to June 8 aboard the Research Vessel Atlantis during the CalNex 2010 field study. In the Los Angeles region, ClNO(2) was more ubiquitous than Cl(2) during most nights of the study period. ClNO(2) and Cl(2) ranged from detection limits at midday to campaign maximum values at night reaching 2100 and 200 pptv, respectively. The maxima were observed in Santa Monica Bay when sampling the Los Angeles urban plume. Cl(2) at times appeared well correlated with ClNO(2), but at other times, there was little to no correlation implying distinct and varying sources. Well-confined Cl(2) plumes were observed, largely independent of ClNO(2), providing support for localized industrial emissions of reactive chlorine. Observations of ClNO(2), Cl(2), and HCl are used to constrain a simple box model that predicts their relative importance as chlorine atom sources in the polluted marine boundary layer. In contrast to the emphasis in previous studies, ClNO(2) and HCl are dominant primary chlorine atom sources for the Los Angeles basin.     

Inactivation of Mycobacterium avium with free chlorine

The inactivation kinetics of Mycobacterium avium with free chlorine was characterized by two stages: an initial phase at a relatively fast rate followed by a slower second stage of pseudo first-order kinetics. The inactivation rate of each stage was approximately the same for all experiments performed at a certain condition of pH and temperature; however, variability was observed for the disinfectant exposure at which the transition between the two stages occurred. This variability was not a function of the initial disinfectant concentration, the initial bacterial density, or the bacterial stock. However, the transition to the second stage varied more significantly at high temperatures (30 degrees C), while lower variability was observed at lower temperatures (5 and 20 degrees C). Experiments conducted at pH values in the range of 6-9 revealed that the inactivation of M. avium was primarily due to hypochlorous acid, with little contribution from hypochlorite ion within this pH range. The inactivation kinetics was represented with a two-population model. The activation energies for the resulting pseudo first-order rate constants for the populations with fast and slow kinetics were 100.3 and 96.5 kJ/mol, respectively. The magnitude of these values suggested that for waters of relatively high pH and low temperatures, little inactivation of M. avium would be achieved within treatment plants, providing a seeding source for distribution systems.     

Stability of caseinate solutions in the presence of calcium

The presence of calcium ions in aqueous solutions of bovine caseinate leads to the formation of large aggregates that precipitate after centrifugation. The residual fraction of soluble casein in the supernatant was measured as a function of the calcium concentration and the total caseinate content. It was found to be determined by the calcium concentration independent of the caseinate concentration. The soluble casein was characterized using light scattering and consisted of small aggregates with a radius of about 12 nm containing about 15 casein molecules. The composition of the soluble casein was determined with chromatography and was increasingly poor in α_s1-casein with increasing calcium content. The solubility of calcium caseinate was determined and related to the total calcium ion concentration.     

Formation of dioxins during the combustion of newspapers in the presence of sodium chloride and poly(vinyl chloride)

Exhaust gases from the combustion of newspaper alone, from branches of London plane tree alone, and from newspapers mixed with sodium chloride (NaCl), polyethylene, or poly(vinyl chloride) (PVC) were collected. The samples were analyzed for dioxins by gas chromatography/mass spectrometry. Total amounts of dioxins found in the samples were 0.186 ng/g from newspapers alone, 1.42 ng/g from the branches of London plane, 102 ng/g from newspapers impregnated with sodium chloride (CI wt % = 3.1), 101 ng/g from newspapers impregnated with sodium chloride mixed with PVC (Cl wt % = 2.6), and 146 ng/g from newspapers mixed with PVC (Cl wt % = 5.1). Samples with a higher chloride content produced more dioxins, and there is a clear correlation between dioxin formation and chloride content. The amount of dioxins formed in the samples according to the number of chlorides was Cl5 > Cl4 > Cl6 > Cl7 > Cl8 in PCDD isomers and Cl4 > Cl5 > Cl6 > Cl7 > Cl8 in PCDF isomers, except in the case of newspapers alone. Benzofurans composed 78-92% of the total dioxins formed in the exhaust gases. The higher the number of the chlorides, the lower the production of benzofuran observed. NaCl vaporized at the temperature of the flame used for combustion of the samples (760-1080 degrees C). The results indicate that NaCl and PVC contribute significantly to dioxin formation from waste materials combusted in incinerators.     

Phenol chlorination and photochlorination in the presence of chloride ions in homogeneous aqueous solution

Phenol chlorination was studied in the presence of dissolved Fe(III) and chloride under irradiation and of hydrogen peroxide and chloride in dark acidic solutions. In the former case phenol photochlorination is most likely due to the formation of Cl2*- as a consequence of Fe(III) irradiation in the presence of chloride. The most efficient pathway is the photolysis of FeOH2+ producing hydroxyl, which oxidizes chloride to Cl*. The latter finally yields Cl2*- upon further reaction with chloride. The importance of the pathway involving FeOH2+ is higher at higher pH and moderately low chloride concentration. At pH 2.0 and [Cl-] > 0.03 M chlorophenol generation rate decreases with increasing [Cl-], due to the formation of the much less photoactive species FeCl2+/FeCl2+. The photolysis of FeCl2+/ FeCl2+ yielding Cl* is likely to play an important role at pH 0.5 and high chloride, but under such conditions chlorophenol formation rates are about an order of magnitude lower than at pH 2.0. Due to pH and kinetic constraints, under most environmental conditions the photochemistry of FeCl2+/FeCl2+ can be expected to play a minor role toward chlorination when compared with the one of FeOH2+, which leads to hydroxyl-mediated chloride oxidation. Hydrogen peroxide and chloride react in dark acidic solutions to yield HClO, involved in electrophilic chlorination processes. Chlorophenol formation rates under such conditions are directly proportional to [H+]. The described chlorination and photochlorination processes can take place in acidic aerosols of marine origin, naturally rich in chloride and Fe(III). Antarctic aerosol is also rich of hydrogen peroxide and often strongly acidic due to the presence of sulfuric acid of biogenic origin.     

Stability of encapsulated olive oil in the presence of caffeic acid

The aim of this study was to investigate the influence of microencapsulation and addition of the phenolic antioxidant caffeic acid (CA) on the storage stability of olive oil. Olive oil in the absence or presence of 300 ppm CA was encapsulated in 1.5% w/w sodium alginate shells. Encapsulated oil (with/without added CA) and unencapsulated oil were stored at 20 or 37 °C for 30 days and then subjected to stability and quality evaluation based on peroxide value (PV), p-anisidine value (p-AV), Totox value, free fatty acid (FFA), total extractable phenolic content (TEPC), and fatty acid composition. The CA addition increased the stability and TPC of the final oil product. Oxidation changes were generally slower in the encapsulated oil samples. Both encapsulation and addition of CA preserved unsaturated fatty acids (UFAs) including C18:1 (omega-9 FA), C18:2 (omega-6 FA) and C18:3 (omega-3 FA). We conclude that the current oil encapsulation method using alginate microspheres could be a feasible approach to increasing olive oil stability. The addition of CA to olive oil not only provides additional protection to the oil, but also improves the nutritional values of the final oil product in terms of elevated TEPC and desired UFAs.     

Some investigations on ASAM pulping and chlorine free bleaching of eucalyptus from spain

In ASAM pulping of eucalyptus important process variables, such as methanol content of the cooking liquor kind of additional alkali source and alkali ratio were investigated. The pulping results were compared to those of kraft cooks carried out with identical raw material. In the bleaching trials the attention was focused on chlorine free sequences. The most meaningful advantage of ASAM pulping in comparison to the kraft process is the easy bleachability of the pulps. The good bleaching response allows the application of an absolutely chlorine free bleaching sequence, without excessively impairing pulp strength.     

桉木硫酸盐浆ECF漂白引入臭氧漂白的效果

巴西桉木浆(巨桉和柳桉)氧脱木素采用了ZDED和DEDD漂白工序。对比ZDED和DEDD漂白工序,计算出的置换率(1k g臭氧可代替的纯二氧化氯量)为2.5~3.5k g,而理论值为1.7kg,表明ZDED漂白工序中无效反应较少。随着臭氧用量的增加,纤维黏度大幅降低(臭氧用量0.8%时,纤维黏度降低50%)。与采用DEDD漂白的桉木浆相比,采用ZDED漂白的桉木浆其他典型特性有:易打浆、保水值低、纤维连接比例高和湿零距裂断长低(仅发生在臭氧用量为0.8%时)。     

Organic acid based sanitizers and free chlorine to improve the microbial quality and shelf-life of sugar snaps

A screening in a sugar snap packaging company showed a converged build-up of aerobic psychrotrophic plate count (APC) (ca. 6.5 log CFU/100 mL), yeasts and molds (Y&M), and lactic acid bacteria (LAB) (both ca. 4.5 log CFU/100 mL) in the wash water in the absence of water sanitizer, and a low build-up of chemical oxygen demand (30 ± 5 mg O₂/L) and turbidity (5.2 ± 1.1 NTU).     

Modeling the kinetics of ferrous iron oxidation by monochloramine

The maintenance of disinfectants in distribution systems is necessary to ensure drinking water safety. Reactions with oxidizable species can however lead to undesirable disinfectant losses. Previous work has shown that the presence of Fe(II) can cause monochloramine loss in distribution system waters. This paper further examines these reactions and presents a reaction mechanism and kinetic model. The mechanism includes both aqueous-phase reactions and surface-catalyzed reactions involving the iron oxide product. In addition, it considers competitive reactions involving the amidogen radical that lead to a nonelementary stoichiometry. Using the method of initial rates, the aqueous-phase reactions were found to have first-order dependencies on Fe(II), NH2Cl, and OH- and a rate coefficient (kNH2Cl,soln) of 3.10 (+/-0.560) x 10(9) M(-2) min(-1). The surface-mediated reactions were modeled by assuming the formation of two surface species: >FeOFe+ and >FeOFeOH. Using numerical techniques, combined rate coefficients for the surface-mediated processes were determined to be 0.56 M(-3) min(-1) and 3.5 x 10(-18) M(-4) min(-1), respectively. The model was then used to examine monochloramine and Fe(II) stability under conditions similar to those observed in distribution systems. Our findings suggest the potential utility of monochloramine as an oxidant for Fe(III) removal in drinking water treatment.     

Comparison of the chlorine inactivation of Yersinia enterocolitica in chlorine demand and demand-free systems

Inactivation of Yersinia enterocolitica by chlorine (0.6 to 20 ppm) was investigated in distilled water and in tryptic soy broth (TSB, 0.015%) at different temperatures (4, 20, and 40 degrees C). In distilled water, chlorine inactivation of Y. enterocolitica was enhanced by increasing the temperature from 4 to 20 degrees C, and survival curves were described by a model that assumed first-order kinetics followed by tailing in which the microbial concentration remained constant. The presence of TSB increased chlorine resistance of Y. enterocolitica, and survival curves were concave downward. These survival curves were described by a model based on the Weibull distribution. Chlorine decay in distilled water was independent of temperature and of the initial concentration of available chlorine and was modeled by first-order reaction kinetics. Chlorine decay in TSB was independent of the initial chlorine concentration but depended on the treatment temperature and was modeled by the addition of two first-order decay equations. The increased resistance of Y. enterocolitica to chlorine in TSB was not due only to the chlorine demand by the TSB components. These components protected Y. enterocolitica cells from the antimicrobial effect of chlorine.     

About presence of free phosphoserine in ripened cheese and in enzymatic hydrolysate of casein

Occurrence of free phosphoserine (SerP) in ripened cheeses was investigated to clarify whether this amino acid can be directly released from casein by enzymatic attack. Free amino acids extracted from cheese were separated by IEC or RP-HPLC and the peak of SerP always eluted close to unretained material and acidic components. Presence of these interferences suggests that the content of free SerP (from 0.8 to 16.4 mmoles/kg cheese) could be highly overestimated. These figures were dramatically lowered (up to 100 times) after a purification step of the cheese extract on cationic column, but the chromatographic separation of SerP was not yet interference-free. However, these values of free SerP are not significant on the basis of the total amount of free amino acids (<0.06%). The interfering compounds were characterized in Grana Padano cheese by FAB-MS and several low-MW peptides were found, the most abundant of which was the casein phosphopeptide (CPP) β(16-22)3P. In vitro enzymatic hydrolysis of casein confirmed that accumulation of short-chain CPPs having the common structure X-SerP-SerP-SerP-Glu-Glu-X occurs, explaining incomplete recovery of the amino acids. The recovery increased from 89% up to 96% and the content of Ser and Glu approached the theoretical value when the enzymatic hydrolysis was performed in presence of alkaline phosphatase. These data are consistent with splitting of Ser and not of SerP from casein by enzymatic attack and with accumulation of only free Ser in cheese ripening. Because of the accumulation of “enzyme-resistant” CPPs, in vitro enzymatic hydrolysis of casein can be completed when alkaline phosphatase is included in the pool of enzymes.     

麦草NaOH-AQ浆短程序TCF漂白的研究

对麦草NaOH-AQ浆短程序（OpQPo）TCF漂白工艺进行了研究。结果表明，H2O2化氧脱木素段（Op）的最佳工艺条件为：浆浓10，H2O2,0.5％，MgSO4 0.5％，用碱量4％，氧压0.6MPa,，温度100℃，时间60～90min；EDTA螯合处理（Q）的适宜工艺条件为：浆浓10％，EDTA用量0.3％，初始pH值3，温度70℃，时间60min；高温高压H2O2漂白（P0）的最适宜工艺条件为：浆浓10％，MgSO4 0.5％，Na2SiO3用量3％，NaOH用量为3％，氧压1．1MPa,，漂白温度110℃，H2O2用量3％，时间60min。在优化条件下，漂终白度达80．2％ISO。